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A monitor or display (sometimes called a visual display unit) is an electronic visual
display for computers. The monitor comprises the display device, circuitry, and an
enclosure. The display device in modern monitors is typically a thin film transistor liquid
crystal display (TFT-LCD), while older monitors use a cathode ray tube (CRT).

   [edit] Screen size
Main articles: Viewable image size and Computer display standard




For any rectangular section on a round tube, the diagonal measurement is also the
diameter of the tube
                                                                                               ·
The area of displays with identical diagonal measurements can vary substantially

The size of an approximately rectangular display is usually given as the distance between
two opposite screen corners, that is, the diagonal of the rectangle. One problem with this
method is that it does take into account the fact that when a rectangle with a given length
to its diagonal, becomes more rectangular, and less square (its aspect ratio increases), and
at the same time its diagonal remains the same, then the area of the rectangle decreases.
That is, given the same diagonal, the area of the display decreases if its aspect ratios
increases. For example, a 4:3 21 in (53 cm) monitor has an area of about 211 sq in
(1,360 cm2), while a 16:9 21-inch widescreen has about 188 sq in (1,210 cm2).

This method of measurement is inherited from the method used for the first generation of
CRT television, when picture tubes with circular faces were in common use. Being
circular, only their diameter was needed to describe their size. Since these circular tubes
were used to display rectangular images, the diagonal measurement of the rectangle was
equivalent to the diameter of the tube's face. This method continued even when cathode
ray tubes were manufactured as rounded rectangles.

Another problematic practice was using the size of a monitor's imaging element, rather
than the size of its viewable image, when describing its size in publicity and advertising
materials. Especially on CRT displays, a substantial portion of the imaging element is
concealed behind the case's bezel or shroud in order to hide areas outside the monitor's
safe area due to overscan. These practices were seen as deceptive, and widespread
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consumer objection and lawsuits eventually forced most manufacturers to instead
measure viewable size.

[edit] Performance measurements
The performance of a monitor is measured by the following parameters:

   ·    Luminance is measured in candelas per square meter (cd/m2 also called a Nit).
   ·    Viewable image size is measured diagonally. For CRTs, the viewable size is
        typically 1 in (25 mm) smaller than the tube itself.
   ·    Aspect ratios is the ratio of the horizontal length to the vertical length. 4:3 is the
        standard aspect ratio, for example, so that a screen with a width of 1024 pixels
        will have a height of 768 pixels. If a widescreen display has an aspect ratio of
        16:9, a display that is 1024 pixels wide will have a height of 576 pixels.
   ·    Display resolution is the number of distinct pixels in each dimension that can be
        displayed. Maximum resolution is limited by dot pitch.
   ·    Dot pitch is the distance between subpixels of the same color in millimeters. In
        general, the smaller the dot pitch, the sharper the picture will appear.
   ·    Refresh rate is the number of times in a second that a display is illuminated.
        Maximum refresh rate is limited by response time.
   ·    Response time is the time a pixel in a monitor takes to go from active (black) to
        inactive (white) and back to active (black) again, measured in milliseconds.
        Lower numbers mean faster transitions and therefore fewer visible image
        artifacts.
   ·    Contrast ratio is the ratio of the luminosity of the brightest color (white) to that of
        the darkest color (black) that the monitor is capable of producing.
   ·    Power consumption is measured in watts.
   ·    Viewing angle is the maximum angle at which images on the monitor can be
        viewed, without excessive degradation to the image. It is measured in degrees
        horizontally and vertically.

[edit] Comparison

[edit] CRT

Pros:

   ·    High dynamic range (up to around 15,000:1 [1],) excellent color, wide gamut and
        low black level.
   ·    Can display natively in almost any resolution and refresh rate
   ·    No input lag
   ·    Sub-millisecond response times
   ·    Near zero color, saturation, contrast or brightness distortion. Excellent viewing
        angle.
   ·    Usually much cheaper than LCD or Plasma screens.

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Cons:

   ·    Large size and weight, especially for bigger screens (a 20-inch unit weighs about
        50 lb (23 kg))
   ·    High power consumption
   ·    Geometric distortion caused by variable beam travel distances
   ·    Older CRTs are prone to screen burn-in
   ·    Produces noticeable flicker at low refresh rates

[edit] LCD

Pros:

   ·    Very compact and light
   ·    Low power consumption
   ·    No geometric distortion
   ·    Rugged
   ·    Little or no flicker depending on backlight technology

Cons:

   ·    Limited viewing angle, causing color, saturation, contrast and brightness to vary,
        even within the intended viewing angle, by variations in posture.
   ·    Bleeding and uneven backlighting in some monitors, causing brightness
        distortion, especially toward the edges.
   ·    Slow response times, which cause smearing and ghosting artifacts. Modern LCDs
        have response times of 8 ms or less.
   ·    Only one native resolution. Displaying resolutions either requires a video scaler,
        lowering perceptual quality, or display at 1:1 pixel mapping, in which images will
        be physically too large or won't fill the whole screen.
   ·    Fixed bit depth, many cheaper LCDs are incapable of truecolor.
   ·    Input lag
   ·    Dead pixels may occur either during manufacturing or through use.

[edit] Plasma

Main article: Plasma display

Pros:

   ·    Compact and light.
   ·    High contrast ratios (10,000:1 or greater,) excellent color, wide gamut and low
        black level.
   ·    High speed response.
   ·    Near zero color, saturation, contrast or brightness distortion. Excellent viewing
        angle.

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   ·    No geometric distortion.
   ·    Highly scalable, with less weight gain per increase in size (from less than 30 in
        (760 mm) wide to the world's largest at 150 in (3,800 mm)).

Cons:

   ·    Large pixel pitch, meaning either low resolution or a large screen.
   ·    Noticeable flicker when viewed at close range
   ·    High operating temperature and power consumption
   ·    Only has one native resolution. Displaying other resolutions requires a video
        scaler, which degrades image quality at lower resolutions.
   ·    Fixed bit depth
   ·    Input lag
   ·    Older PDPs are prone to burn-in
   ·    Dead pixels are possible during manufacturing

[edit] Problems
[edit] Phosphor burn-in

Phosphor burn-in is localized aging of the phosphor layer of a CRT screen where it has
displayed a static bright image for many years. This results in a faint permanent image on
the screen, even when turned off. In severe cases, it can even be possible to read some of
the text, though this only occurs where the displayed text remained the same for years.

This was once a common phenomenon in single purpose business computers. It can still
be an issue with CRT displays when used to display the same image for years at a time,
but modern computers are not normally used this way anymore, so the problem is not a
significant issue. The only systems that suffered the defect were ones displaying the same
image for years, and with these the presence of burn-in was not a noticeable effect when
in use, since it coincided with the displayed image perfectly. It only became a significant
issue in three situations:

   ·    when some heavily used monitors were reused at home,
   ·    or re-used for display purposes
   ·    in some high-security applications (but only those where the high-security data
        displayed did not change for years at a time).

Screen savers were developed as a means to avoid burn-in, but are unnecessary for CRTs
today, despite their popularity.

Phosphor burn-in can be gradually removed on damaged CRT displays by displaying an
all-white screen with brightness and contrast turned up full. This is a slow procedure, but
is usually effective[citation needed].


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[edit] Plasma burn-in

Burn-in re-emerged as an issue with early plasma displays, which are more vulnerable to
this than CRTs. Screen savers with moving images may be used with these to minimize
localized burn. Periodic change of the color scheme in use also helps.

[edit] Glare

Glare is a problem caused by the relationship between lighting and screen, or by using
monitors in bright sunlight. Matte finish LCDs and flat screen CRTs are less prone to
reflected glare than conventional curved CRTs or glossy LCDs, and aperture grille CRTs,
which are curved on one axis only and are less prone to it than other CRTs curved on
both axes.

If the problem persists despite moving the monitor or adjusting lighting, a filter using a
mesh of very fine black wires may be placed on the screen to reduce glare and improve
contrast. These filters were popular in the late 1980s[citation needed]. They do also reduce
light output.

A filter above will only work against reflective glare; direct glare (such as sunlight) will
completely wash out most monitors' internal lighting, and can only be dealt with by use
of a hood or transreflective LCD.

[edit] Color misregistration

With exceptions of correctly aligned video projectors and stacked LEDs, most display
technologies, especially LCD, have an inherent misregistration of the color channels, that
is, the centers of the red, green, and blue dots do not line up perfectly. Sub-pixel
rendering depends on this misalignment; technologies making use of this include the
Apple II from 1976[1], and more recently Microsoft (ClearType, 1998) and XFree86 (X
Rendering Extension).

[edit] Incomplete spectrum

RGB displays produce most of the visible color spectrum, but not all. This can be a
problem where good color matching to non-RGB images is needed. This issue is common
to all monitor technologies with three color channels.

[edit] Display interfaces
[edit] Computer terminals

Main article: Computer terminal



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Early CRT-based VDUs (Visual Display Units) such as the DEC VT05 without graphics
capabilities gained the label glass teletypes, because of the functional similarity to their
electromechanical predecessors.

Some historic computers had no screen display, using a teletype, modified electric
typewriter, or printer instead.

[edit] Composite signal

Early home computers such as the Apple II and the Commodore 64 used a composite
signal output to drive a CRT monitor or TV. This resulted in degraded resolution due to
compromises in the broadcast TV standards used. This method is still used with video
game consoles. The Commodore monitor had S-Video input to improve resolution.

[edit] Digital monitors

Early digital monitors are sometimes known as TTLs because the voltages on the red,
green, and blue inputs are compatible with TTL logic chips. Later digital monitors
support LVDS, or TMDS protocols.

[edit] TTL monitors




IBM PC with green monochrome display.

Monitors used with the MDA, Hercules, CGA, and EGA graphics adapters used in early
IBM PC's (Personal Computer) and clones were controlled via TTL logic. Such monitors
can usually be identified by a male DB-9 connector used on the video cable. The
disadvantage of TTL monitors was the limited number of colors available due to the low
number of digital bits used for video signaling.

Modern monochrome monitors use the same 15-pin SVGA connector as standard color
monitors. They are capable of displaying 32-bit grayscale at 1024x768 resolution,
making them able to interface with modern computers.

TTL Monochrome monitors only made use of five out of the nine pins. One pin was used
as a ground, and two pins were used for horizontal/vertical synchronization. The electron

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gun was controlled by two separate digital signals, a video bit, and an intensity bit to
control the brightness of the drawn pixels. Only four shades were possible; black, dim,
medium or bright.

CGA monitors used four digital signals to control the three electron guns used in color
CRTs, in a signaling method known as RGBI, or Red Green and Blue, plus Intensity.
Each of the three RGB colors can be switched on or off independently. The intensity bit
increases the brightness of all guns that are switched on, or if no colors are switched on
the intensity bit will switch on all guns at a very low brightness to produce a dark grey. A
CGA monitor is only capable of rendering 16 colors. The CGA monitor was not
exclusively used by PC based hardware. The Commodore 128 could also utilize CGA
monitors. Many CGA monitors were capable of displaying composite video via a
separate jack.

EGA monitors used six digital signals to control the three electron guns in a signaling
method known as RrGgBb. Unlike CGA, each gun is allocated its own intensity bit. This
allowed each of the three primary colors to have four different states (off, soft, medium,
and bright) resulting in 64 colors.

Although not supported in the original IBM specification, many vendors of clone
graphics adapters have implemented backwards monitor compatibility and auto detection.
For example, EGA cards produced by Paradise could operate as an MDA, or CGA
adapter if a monochrome or CGA monitor was used in place of an EGA monitor. Many
CGA cards were also capable of operating as MDA or Hercules card if a monochrome
monitor was used.

[edit] Single color screens

Display colors other than white were popular on monochrome monitors in the 1980s.
These colors were more comfortable on the eye. This was particularly an issue at the time
due to the lower refresh rates in use at the time causing flicker, plus the use of less
comfortable color schemes than used with most of today's software.

Green screens were the most popular color, with amber displays also available. "Paper
white" was also in use, which was a warm white.

[edit] Modern technology
[edit] Analog monitors

Most modern computer displays can show the various colors of the RGB color space by
changing red, green, and blue analog video signals in continuously variable intensities.
These have been almost exclusively progressive scan since the middle 1980s. While
many early plasma and liquid crystal displays have exclusively analog connections, all
signals in such monitors pass through a completely digital section prior to display.

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While many similar connectors (13W3, BNC, etc…) were used on other platforms, the
IBM PC and compatible systems long ago standardized on the VGA connector.

[edit] Digital and analog combination

The first popular external digital monitor connectors, such as DVI-I and the various
breakout connectors based on it, included both analog signals compatible with VGA and
digital signals compatible with new flat-screen displays in the same connector.

[edit] Digital monitors

Newer connectors are being made which have digital only video signals. Many of these,
such as HDMI and DisplayPort, also feature integrated audio and data connections. One
less popular feature most of these connectors share are DRM encrypted signals.

[edit] Configuration and usage
[edit] Multiple monitors

Main article: Multi-monitor

More than one monitor can be attached to the same device. Each display can operate in
two basic configurations:

   ·   The simpler of the two is mirroring (sometimes cloning,) in which at least two
       displays are showing the same image. It is commonly used for presentations.
       Hardware with only one video output can be tricked into doing this with an
       external splitter device, commonly built into many video projectors as a pass
       through connection.
   ·   The more sophisticated of the two, extension allows each monitor to display a
       different image, so as to form a contiguous area of arbitrary shape. This requires
       software support and extra hardware, and may be locked out on "low end"
       products by crippleware.
   ·   Primitive software is incapable of recognizing multiple displays, so spanning
       must be used, in which case a very large virtual display is created, and then pieces
       are split into multiple video outputs for separate monitors. Hardware with only
       one video output can be made to do this with an expensive external splitter
       device, this is most often used for very large composite displays made from many
       smaller monitors placed edge to edge.

[edit] Multiple video sources

Multiple devices can be connected to the same monitor using a video switch. In the case
of computers, this usually takes the form of a "Keyboard Video Mouse switch" (KVM)


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switch, which is designed to switch all of the user interface devices for a workstation
between different computers at once.

[edit] Virtual displays

Main article: Virtual desktop Screenshot of workspaces layed out by Compiz

Much software and video hardware supports the ability to create additional, virtual pieces
of desktop, commonly known as workspaces. Spaces is Apple's implementation of
virtual displays.

[edit] Additional features
[edit] Power saving

Most modern monitors will switch to a power-saving mode if no video-input signal is
received. This allows modern operating systems to turn off a monitor after a specified
period of inactivity. This also extends the monitor's service life.

Some monitors will also switch themselves off after a time period on standby.

Most modern laptops provide a method of screen dimming after periods of inactivity or
when the battery is in use. This extends battery life and reduces wear.

[edit] Integrated accessories

Many monitors have other accessories (or connections for them) integrated. This places
standard ports within easy reach and eliminates the need for another separate hub,
camera, microphone, or set of speakers.

[edit] Glossy screen

Main article: Glossy display

Some displays, especially newer LCD monitors, replace the traditional anti-glare matte
finish with a glossy one. This increases saturation and sharpness but reflections from
lights and windows are very visible.

[edit] Directional screen

Narrow viewing angle screens are used in some security conscious applications.

[edit] Autopolyscopic screen

Main article: Autostereoscopy
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A directional screen which generates 3D images without headgear.

[edit] Touch screen

These monitors use touching of the screen as an input method. Items can be selected or
moved with a finger, and finger gestures may be used to convey commands. The screen
will need frequent cleaning due to image degradation from fingerprints.

[edit] Tablet screens

Main article: Graphics tablet/screen hybrid

A combination of a monitor with a graphics tablet. Such devices are typically
unresponsive to touch without the use of one or more special tools' pressure. Newer
models however are now able to detect touch from any pressure and often have the ability
to detect tilt and rotation as well.

[edit] Major manufacturers
   ·   Acer
   ·   AOC
   ·   Apple Inc.
   ·   Asus
   ·   BenQ
   ·   Dell
   ·   Eizo
   ·   Gateway
   ·   Hewlett-Packard
   ·   HannStar Display Corporation
   ·   Iiyama Corporation
   ·   LG
   ·   NEC
   ·   Samsung
   ·   Sony
   ·   Toshiba
   ·   Tyco Electronics
   ·   ViewSonic




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